Objects don't follow the particles system/vertex group
This may be because of a thing where in blender 2.80 and up, auto cache refreshing got scrambled. First it refreshed when it shouldn't've, now it has sometimes not been refreshing when it should've: You probably need to refresh the particle cache manually.
One way that seems fairly solid is change some fundamental setting to the particles/simulation, then immediately change it back. Number of particles is one, particle size is not.
This is just a guess, I hope it helps.